Field of the Invention
This invention relates to a process of converting non-distillable residues of mixed-base or paraffin-base crude hydrocarbon oils to distillable precursors for motor fuels and/or petrochemical products by donor solvents hydrovisbreaking at temperatures of 380.degree. to 480.degree. C. and pressures of 40 to 200 bars in the presence of a circulated hydrogen donor solvent which has been produced in the same process and in the presence of hydrogen and by a succeeding distillation to separate the hydrogenated liquid hydrocarbons into a plurality of fractions.
It is known that heavy hydrocarbon oils having a high content of non-distillable residues can be processed by treating the heavy hydrocarbon oil to elevated temperatures and superatmospheric pressures, if desired, in the presence of dispersed solids, with molecular hydrogen and a circulated hydrogen donor oil. The process can be performed such that a certain proportion of the asphaltenes adsorbed to the solids are coked. Thereafter, the product of that donor solvent hydrovisbreaking (DSV) is distilled, the distillate or distillates is or are catalytically hydrogenated, the visbreaker residue is made available for the production of hydrogen, and the hydrogenated products are divided into fractions, which are processed further to form motor fuels and/or petrochemical products (see German Offenlegungsschrift 29 20 415).
It is also known to carry out the treatment of the crude oil near the coking limit in the presence of hydrogen donor components which have been derived from the crude oil itself or from a similar crude oil or from the visbreaker distillate (see German Offenlegungsschrift 29 49 935).
These known processes can be used to produce, under steady-state conditions, from naphthenic crude oils a hydrogen donor solvent having the approximate composition C (aliphatic) up to 50%, C (naphthenic) at least 35%, and C (aromatic) at least 15% and having a boiling range from 200.degree. to 500.degree. C. Owing to its good hydrogen-transferring properties, that product may be recycled to the hydrovisbreaker. The hydrogen donor solvent acts not only to maintain or even improve the asphaltenes in colloidal solution in the raw material to be processed but also makes the hydrogen available under the prevailing reaction conditions at a rate which at any time substantially matches the rate at which the raw material is hydrogenated. As a result, the recombination of the hydrogen radicals to form molecular hydrogen is minimized. Owing to these properties, the recycling of the hydrogen donor solvent to the hydro-visbreaker permits a conversion of the starting residue of more than 90% and while permitting use of such small amounts of donor solvent compared to the starting residue that undesired isomerization of the hydrogen-transferring components is avoided.
However, in the conversion of non-distillable residues of mixed-basic or paraffinic crude hydrocarbon oils, a hydrogen donor solvent having the desired composition and desired properties cannot be produced and circulated in the same process because under steady-state conditions the concentration of aromatic and naphthenic compounds are too low and the concentration of aliphatic compounds is too high.
It is an object of the invention, therefore, to provide a process for hydrogen donor solvent visbreaking which avoids these disadvantages of the prior art and ensures very low concentrations of aromatic and napththenic compounds so that a hydrogen donor solvent of high quality is obtained which when recycled to the hydrovisbreaking process permits an optimum conversion of non-distillable residues of mixed-basic or paraffin-basic crude hydrocarbon oils to form useful precursors for use in the production of power or of raw materials.